Means for and method of scrambling speech signals



G. GUANELLA 2,510,338

MEANS FOR AND METHOD 0E SCRAMELING SPEECH SIGNALS June 6, 1950 2Sheets-Sheet 1 Filed Sept. 5, 1946 alumdwy lNvENToR G'z/srnv Gun/VELE LJi@ ATTORNEY June 6, 1950 G. GUANELLA 2,510,338

MEANS EoR AND METHOD oE SCRAMBLING SPEECH SIGNALS Filed Sept. 5, 1946 2SheetsSheet 2 /m/L T/ FREQUENCY GENE/En Toe INVENTOR Gusrnv Guan/gun ZMi@ ATTORNEY Patented June 6, 1950 'FET MEANS FOR AND METHOD OFSCRAMIBLING SPEECH SIGNALS Gustav Guanella, Zurich, Switzerland,assignorV to Radio Patents Corporation, New York, N. Y., a corporationof New York Application September 5, 1946, Serial No. 695,030 InSwitzerland September 15, 1945 mission, into a plurality of frequencysub-bands,

which are interchanged by the aid of auxiliary displacement carrieroscillations in their relative positions within the original frequencyband. Additionally, the frequencies of one or more subbands may beinverted by known means to increase the degree of secrecy obtained.

The present invention also relates to a scrambling method of thisgeneral type known as frequency substitution scrambling, and has for itsmain object to further increase the degree of secrecy obtained and tosubstantially prevent the deciphering or decoding of a scrambled messageby an unauthorized listener or receiver.

With this general object in view, the invention involves basically thesubdivision of a given signal frequency band, such as a speech frequencyband, into a plurality of sub-bands which are mutually interchanged inaccordance with the substitution scrambling method.

According to the present improvement, the thus obtained scrambledfrequency band is divided into at least two secondary or partialfrequency ranges which are mutually interchanged and at least one ofwhich may be inverted, said secondary frequency ranges being so relatedto the primary scrambling sub-bands that their common limit orseparating frequency or frequencies coincide with a frequency within oneof said sub-bands. In other words, the limit or separating frequency ofthe partial ranges should not coincide with any of the limit frequenciesof the primary scrambling sub-bands, as will become further evident fromthe following.

The invention, both as to its further objects and novel aspects, willbecome more apparent from the following detailed description taken inreference to the accompanying drawings forming part of thisspecification, and wherein:

Fig. 1 is a theoretical diagram illustrating the successive steps ofconverting a given speech frequency band into a final scrambled band inaccordance with the invention.

Fig. 2 shows a practical system in block diagram form for carrying intoeffect the scrambling method illustrated in Fig. 1.

Figs. 3 and 4 are partial diagrams illustrating,

respectively, a. preferred multi-frequency gen-v erator and modulator orfrequency transposing device suitable for use in connection with theinvention.

Referring more particularly to Fig. 1, wherein the abscissae along thevarious horizontal lines represent frequency and the ordinates representamplitude, an original speech frequency band a covering a range from 300cycles to 2,700 cycles, which has been found in practice to be fullysufcient' for the transmission of intelligible speech, is at firsttransposed or shifted to the range between 8,300 and 10,700 cycles bymodulating it in the modulator M1, Fig. 2, upon an auxiliarydisplacement carrier oscillation u1 supplied by a multi-frequency orharmonic generator G and having a frequency f,1=8,000 cycles. Bysegregating, by means of band pass lter F1, the upper side band from theoutput of modulator M1, the frequency band b is obtained in a mannerwell understood. The frequency band b is in turn subjected to a furthermodulation in the modulator L@ to which are applied in succession bymeans of a distributor U six auxiliary oscillations ua, ul ua alsosupplied by the harmonic generator G and having frequencies f3= 7,600cycles, j4=7,200 cycles, f5=6,800 cycles, fs=6,400 cycles, f1=6,000cycles, fa=5,600 cycles. respectively.

In order to increase the degree of secrecy, it is desirable to changethe sequence of application of the auxiliary oscillations ua, u4 ua tothe modulator M2 by correspondingly connecting the distributor contactsto the supply leads from the generator G.

As a result of the modulation in modulatorl M2, periodic lower sidebands c1, cz ce are obtained successively displaced relative to theoriginal band a by differences of 1/6 of the latter, i. e., equal to 400cycles. The signal bands c1, c2 es are amplified in a standard amplifierA1. Each of the amplied signal frequency bands c1, c2 c3 is then dividedinto two partial frequency ranges separated at the fixed or separatingfrequency t, the latter amounting to 2,900 cycles, in the example shown.This separation is effected by means of an electrical switch consistingin the case illustrated of two filters F2 and F3 connected in paralleland having frequency passing ranges adjoining each other at the commonseparating frequency t. Filters F2 and F3 may be band-pass or low-passand highpass lters, respectively, of known design, as is readilyunderstood. 4An essential requirement to obtain a high degree of secrecyis the fact that within each of the frequency bands c1, c2 c6 thereexists a different ratio between the partial ranges produced inaccordance with the above. In other Words, the individual frequencybands c1, c2 .ce is displaced periodically relative to the fixedfrequency t in the manner clearly seen from the drawing.

According to the next step, the partial frequency ranges or primarysubgbands containingv the lower frequencies of the bands c1, c2 .cs arein turn intermodulated in the modulator M3 with a further auxiliaryoscillation 'uz supplied by the generator G and having a fixed frequencyf2=ll,2)o cycles in the example illustrated. The' resulting lower andaccordingly Vinyerted side bands obtained from this modulation are seg-fregated by means of a band-pass filter F4.

Furthermore, the partial ranges or 'primary sub-bands .of higherfrequency of the speech frequency bands ci', jcz ce are again inter- Vnoulated the :modulator Mtv-lith the respectite aukiliary'os'cillations"us, '1 4 L. u8 and the upper side bands' ofthe'modulation product alsosegregated by the band-pass filter F4. "n'this er, the'putput vvo`f";tiltrF4 supplies the six Ky inverted'speech' frequency bands d1, yde all falling` within'the" 'same frequency range of '8,300to'10,"7'00cycles, corresponding to thipas'rsig ranglebf tl''el `nF4. Asis understood; the "prirraiy""" b-#band's "of the frequency ff' CfifC'z,cf y'brflitually nt'el'changed by meansl of any'onfe' 'f 'the''lz'nwnmethods and devlces to 'increase th degree of secrecy obtained..v `Forthe sake'b'f simplic'ty, there nas'been inustrateain rigl ozliytnecm1-ef scrambling of tue'split or d edfreduency tand di', it beingunderstood 'that'tue fart r scrambling or the bands d1; cada.' d5; anddi; takes 'place in a substantiall'y analogousl manner'. The frequencybanaal-is again period iyishiftedrto'diffrent frequency 'range's'tyintermodiilating' it "in 'the paralisi demented ,modul-attrs Ma; Ma; Ms;en with auxiuarysenlations *ui tia; whereby ther-)wer met .a are bb;ta'i'n d'which are nu ally displaced 'by 'a dise iatis; equal tonessifgtri'lf H lf'F-,G ll'yxbad lQV I'* respondng'ttheb'a disci" dc."S'blba'll'sf gwn gg g, each falling within the. range of 270g-aloecycles, are uien sieg gated `fromcada offthe frequent:v lo 'd'sfifcz'.iffeby .means of identical bandepass l'te'rslaaf F515" Fei,"respectively. sub-bands' ci," c@ arie 'in turn'shifted to produce an 'ady 'inmfg' frequency band by modulation With 'the `a li'ary 'oscillationsul. .u8 in "the "m cratersV` Ma, Ma .'Mef, respectively. thismannenthefinal and completely scrambled frequency 'bandit falling Withinthe'all'g Vf' 8,3100'to' 10,700 yles is obtained. VThe finalvsc'ra'znbl'ed frequency bandy h, in addition' to 'its sub-divisioninto! 'a 'pairof primarylsub-bands, oriifof which isinverteu, is thusadditionally divided into a relatively larger numberofsecondarysu'bbant''s gi, y2' gs, in suc'ha manner thatthelimitfrequencies of -said secondary'sub-'bands each coincidfswitli anni#ter'mefd'iate frequency 'of 'the primary -sub-'bands oryn other words,that the' separating Vfrequency' of the Cprimary sub-"bands "coincidessequentially and "pel'dcally'lwith' a predetermined inter; mediate suchvasfthe center Jfrequency of different secondary subeb'ands gi; g2

' 6. 'Since ytlfie`sepa'rating frequency of 2,900 cycles in ItheeX-ample' illustrated at'whic'h the frequency 4 bands c1, cz ce aresplit or divided is exactly in the center of the frequency range of2,700 to 3,100 cycles, which corresponds to the passing range of thefilters F511, Feb Fsf, the subband g4 in the nal scrambled signal iscomlised of two Isublloan'd portions orlarflgesrgli and 14" each havinga bandwidth equal to 200 cycles. .YFurthermore, in the exampleillustrated, subba-'nd portion g4 is uninverted, While sub-band ponticnfyi jisvigxryerted and contains the lowest q ,i equencies of theoriginal speech frequnecy band g. An essential condition for theattainment of crecyV is the fact that the lowest s which arepredominantly e intelligibility of speech are always cohtainedin thesub-band portion g4 of only i200 cycles band Width.

lt. is .understood that the separating frequency tlnay' b'e so chosen asto coincide with any other 2o frsqueey Within the, frequency .range Qfthe Fsc, F51; F5f. lattecafs 13h@ subband Vpcqrrtli'ons 'g4' and g4"will 4be ofr unequai and the con ons are advantageously =so chosenhatthe su and prtionjghas a nar rower :width tharitlh'e Is1.jll3'lca`nd. portion g4.

The teme Sffemliin' as decibs'd "in connection With the speechVfr'eq-rient'y' bands di 'will occur with. @little-ether bands d l'for'instan'ce, 'in the case ofthe 1of,1'lnds'v ds and d; the @respondingSub-tenet [ya adf 'ya rasee@ tively, vin the rfinal Vs cranitljeclYsignal h will be divided into corresponcli g subeband portions, as

4tlf'reir sequence Scrambled 'Speech signal, band h is,

shown 'to be a pied vto Va 'further ampli''er'Az followed by a ben '-PSSmi@ .Ffhyin'g'a pssie frequency range'of 8139@ @790 cycles. Finally',the flieqncy "bend h is Sebi-@cieli t a ``frthr iliary lsvrllatibnh-rto" return it to the original low 'frequency range :ofA"ill22;;(00 cycles corre-l '111'Q0n dividedintoa rilv A l changedlsub-"bands to, Hoducje .a final scrambled signal. ,As is understood,trie` sequence of `operatin trav be 'reverted that is the initial band.may 'be'rst subjected {tosubsm onscrainbling 15 -rby dividing it into aplurality'o 'sub-bands. and

ity olf-.mutually inten d2, da, d5, de. Thus,'

Asare'sult, the subiV r `M7 with the 'auxthe' same conversion steps as dscribed'but :in rel the thus scrambled signal then split into the twopartial ranges in accordance with the present invention. It isfurthermore possible to separate a scrambled signal comprising apluralityl of interchanged sub-bands obtained by a substitution method,into more than two partial ranges, care being taken in accordance withthe invention that the limit frequencies of said partial ranges do notcoincide with any of the limit frequencies of the primary sub-bands inorder-V to obtain the novel effects and increased degree of secrecy inaccordance with the invention.

It is also possible to utilize the arrangementv described in such amanner that the speech frequency band is repeatedly or successivelyseparated into partial .ranges to secure an addedsecrecy. y A

The various elements and parts required for carrying the invention intoeffect may be of standard design and construction well known in the art.This applies especially to the lters and amplifiers, all of which arecommon and standard equipment in communication systems. Themulti-frequency generator -G may also be of any known construction. Asuitable form of such generator is shown in Fig. 3, comprising a tuningfork Oscillator O feeding a harmonic generator A3 in the form of avacuum tube amplifier designed and operated to produce a highlydistorted output wave form, such as by the provision ofa high negativegrid bias, as indicated in the drawing. By means of a plurality offilters N1, N2 Ns connected in the plate circuit of theA tube, theauxiliary frequencies u1, u2 us are derived from the harmonic spectrumin the anode current. Y

The various modulators used for shifting or transposing the frequencybands to desired points on the frequency scale` may also be of any typeknown'in the art. A-specially suitable form of modulator-.is shown inFig. 4,-comprising a balanced circuit of dry-rectiers, such as those ofthe copper oxide or selenium type well known in the art, wherein one ofthe signals to be intermodulated is applied toterminals l, l and theother signal is applied t0 terminals 2, 2', theA resultant product oroutput being derived from' terminals 3, 3' in a manner well known.

While I have shown and described a desirable embodiment of my invention,it is understood that this disclosure is for the purpose of illustrationand that various changes and substitutions of equivalent steps andelements for those herein shown and described may be made withoutdeparting from the spirit and scope of the invention as definedv in theappended claims. The specification and drawings are accordingly to beregarded in an illustrative rather than a limiting sense.

- I claim:

LA system for secret transmission of speech' comprising means forsequentially and periodically producing from an original speechfrequency band a plurality of equal components eachl displaced Awithrespect to the next one by equal frequency ranges being a fraction ofthe total band width of one over the number of components produced,means for splitting of said components into two partial frequency rangesatv a common andY xed separting frequency, furtherpmeans for shiftingthe respective partial ranges into a common frequency range of bandwidth' :equal *to the;v original speech n frequency bandfandwith'one ofsaid partial frequency ranges" being inverted, to produce a plurality ofpre-scrambled frequency bands comprising par-lk tial ranges of varyingrelative width, means for,

in turn producing from each `of said prescrambled frequency bands aplurality of relatively 'displaced components coinciding respectivelywith said first-mentioned components, band-pass filter means forsegregating from said last-mentioned component equal bands of limitedwidth equal to the above-mentioned fraction of the total originalfrequency band and having upper and'lower limit frequencies lying atboth sides of said separating frequency, and means for unequallyshifting the bands selected by said filter meansto positions so as toadjoin each otherand toA form a final scrambled signal of band widthlequalto the original speech frequency band.

' 2. A system for secret transmission of speech comprising means forsequentially and periodi` cally producing from an original speechfrequency band-a plurality of equal components each displaced withrespect to the next one by equal frequency ranges being a fraction ofthe total band- Width ofA one over the number of components *L produced,means forsplitting of said components into Vtwo partial frequency rangesat a common and fixed separating frequency, further means for shiftingthe respectivepartial ranges into a.V

common frequency range of band Width equal to the originalspeech'frequency band and with one-i of said partial frequency rangesbeing inverted, to

producea plurality ofv sequential pre-scrambledr frequency bandscomprising partial ranges ofvarying relative width, means for in turnpro-- separating frequency, and means forunequallyl shifting the bandsselected by said filter means to positions so as to adjoin each otherand to form a final scrambled signal of band width equal' to theoriginal speech frequency band.

3.`A system for secret transmission of speech comprising means forsequentially and periodically producing from an original speechAfrequency band a plurality of equal components each displaced withrespect to the next one by equal frequency ranges being a fraction ofthe total band width of one over the number of components produced,means for splitting of said components into two partial frequency rangesat a common and fixed separating frequency, further means for shiftingthe respective partial ranges into a` common frequency range of bandwidth equal to the original speech frequency band and with one of saidpartial frequency` ranges being inverted, to produce a plurality of`sequential prescrambled frequency bands comprising partialI ranges ofvarying relative width, means for in turn producing from each Vof saidpre-scrambled frequency bands a plurality of relatively displacedcomponents coinciding respectively with said first-mentioned components,band-pass filter means for segregating from said last-mentionedcomponents equal bands of limited width equal to the.above-mentioned...fraction of l the totalv original frequency band andhaving upper andlower Vlimitfrequencies *equally spaced [from saidseparating frequency, `and@ inearis'ic'nl unequaliyl tabak bend.Y Widthaofi/9.11; QYIL components prpdueedfme madre@ f que-miesen ,5, A

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v neisglqallse .lamme '0.131 Qfjseisgprimerx selbe-20211.11@sA secretsignalling compr-is gg ne @semen signal @mehr ad axldmm requeneye. 14. ASmeer/Eigaeetrmnsmsiengoierregen.

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dlenentlntermediategfrequencx.ofnsaid@fprimara Sutrebands.

for periodically varying the interchanging code of said secondarysub-bands.

16. A system for secret transmission of speech comprising scramblingmeans for subdividing a given speech frequency band into a pair ofprimary sub-bands, means for frequency inverting one of said sub-bands,means for sequentially and periodically varying the relative band Widthof said primary sub-bands further means for additionally dividing thepre-scrambled frequency band into a number greater than two of secondaryfrequency sub-bands the limit frequencies of which coincide withdiierent intermediate frequencies of said primary sub-bands, means forfrequency inverting part of said secondary frequency bands, furthermeans for sequentially and periodically varying the relative band widthof said primary sub-bands, and means operated in synchronism with saidlast mentioned means for varying the interchanging code of saidsecondary sub-bands.

17. The method of secret signalling consisting in subdividing, bysequential steps of frequency substitution scrambling, a given signalfrequency band into groups of different numbers of partially invertedfrequency sub-bands, the limit frequencies of the sub-bands resultingfrom one scrambling step coinciding with intermediate frequencies of thesub-bands resulting from another scrambling step.

18. A system for secret transmission of speech comprising scramblingmeans for subdividing a given speech frequency band into a pair ofprimary sub-bands, means for frequency inverting one of said sub-bands,further means for additionally dividing the pre-scrambled frequency bandinto a number greater than two of partially inverted secondary frequencysub-bands, means for sequentially and periodically varying the relativeband width of said primary frequency subbands whereby the separatingfrequency of said primary sub-bands successively coincides with thecenter frequencies of different secondary subbands, and further meansoperated in synchronism with said last-mentioned means for varying theinterchanging code of said secondary sub-bands.

GUSTAV GUANELLA.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,725,566 Chesnut Aug. 20, 19292,301,455 Roberts Nov. 10, 1942 2,402,059 Craib June 11, 1946 2,411,206Guanella Nov. 19, 1946 2,411,683 Guanella Nov. 26, 1946

